To figure the internal drive ratio of your car you divide the number of teeth on the diff gear by the number of teeth on the drive pulley.
Example: 32 teeth on diff gear divided by 18 teeth on the drive pulley. 32/18 = 1.77 internal drive ratio
Final drive ratio is spur gear divided by pinion times internal drive ratio.
Example: 128/32*1.77 = 7.08
Rollout is tire diameter times Pi(3.14) divided by final drive ratio.
Example: 2.28*3.14/7.08 = 1.01
Hope this helps,